An image processing apparatus generates, for an image, partial histograms by dividing a luminance histogram at downward convex parts of a frequency distribution of the luminance histogram. The image processing apparatus calculates, for a partial histogram selected from the partial histograms, a difference between a maximum frequency in each of all the partial histograms located on the first side of the selected partial histogram, and a minimum frequency within a luminance range from a luminance level of the maximum frequency to that of a maximum frequency in the selected partial histogram as a drop, and sets a maximum one of the drops calculated for the respective partial histograms as a drop. The image processing apparatus sets a weight, which becomes smaller as this drop is larger, for the selected partial histogram, and calculates a weighted average of the luminance histogram, thereby acquiring a luminance value for the tone correction.